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POPass unevaluated commands to a function in R
 

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    <p>I am a bit of an R novice, and I am stuck with what seems like a simple problem, yet touches pretty deep questions about how and when things get evaluated in R.</p> <p>I am using Rserve quite a bit; the typical syntax to get things evaluated remotely is a bit of a pain to type repeatedly:</p> <pre><code>RSeval(connection, quote(try(command))) </code></pre> <p>So I would like a function r which does the same thing with just the call: </p> <pre><code>r(command) </code></pre> <p>My first, naive, bound to fail attempt involved: </p> <pre><code>r &lt;- function(command) { RSeval(c, quote(try(command))) } </code></pre> <p>You've guessed it: this sends, literally, <code>try(command)</code> to my confused Rserve daemon. I want <code>command</code> to be <strong>partially</strong> evaluated, if that makes any sense -- i.e. replaced by what I typed as an argument, but <strong>without</strong> evaluating it locally.</p> <p>I looked for solutions to this, browsed throught the documentation for quote, substitute, eval, call, etc.. but I was not able to find something that worked. Either <code>command</code> gets evaluated locally, or not at all.</p> <p>This is not a big problem, I can type the whole damn <code>quote(try())</code> thing all the time; but at this point I am mostly curious as to how to get this to work!</p> <p>EDIT: More explanations as to what I want to do.</p> <ul> <li>In the text above, <code>command</code> is meant to be a call do a function, ideally -- i.e., not a character string. Something like <code>a &lt;- 3</code> or <code>assign("a", 3)</code> rather than <code>"a&lt;-3"</code> or <code>quote(a&lt;-3)</code>. I believe that this is part of what makes this tricky. It seems really hard to tell R not to evaluate this locally, but only send it literally. Basically I would like my function to be a bit like <code>quote()</code>, which does not evaluate its argument.</li> <li>Some explanation about my intentions. I wish to use Rserve frequently to pass commands to a remote R daemon. The commands would be my own (or my colleagues) and the daemon protected by firewall and authentication (and would not be run as root) -- so there is no worry of malicious commands being passed.</li> <li>To be perfectly honest, this is not a big issue, and I would be pretty happy to always use the <code>RSeval(c, quote(try()))</code>. At this point I see this more like an interesting inquiry into the subleties of R :-)</li> </ul>
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    1. COYou might want to read my attempt to explain how to control evaluation in R and some of the pitfalls therein: https://github.com/hadley/devtools/wiki/Evaluation
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